5 Alien Parasites and Their Real-World Counterparts

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Paranoid about parasites? Best avoid the upcoming film
"Prometheus," a quasi-prequel to the 1979 horror film "Alien"
that hits American theaters June 8.

The "Alien" franchise is responsible for giving the world one of
the ugliest alien parasites ever, the bloody "chestburster" that
soon grows into a deadly hunter. But director Ridley Scott isn't
the only moviemaker to look to parasites for inspiration when
creating terrifying space monsters. Here's a look at the
parallels between real-world parasites and Hollywood aliens.

1. Mind Control to Major Tom

Film directors love their mind-controlling parasites. Stargate
SG-1 provides a particularly icky example: the Goa'uld Symbiote,
a snake-like creature that penetrates its host's neck and wraps
itself around the spine, taking over control.

Goa'uld are evil, arrogant creatures with a plan for galactic
domination. Real-life parasites don't share those goals (as far
as we know…) but many are capable of mind control. One creepy
example, Ophiocordyceps unilateralis, is a fungus that
attacks ants. Once it invades an ant, the fungus compels the poor
insect to scramble down to low leaves, finally biting a vein on
the underside of a perfectly placed leaf. Having done its job,
the
"zombie" ant then dies. To make matters worse, its body
becomes a greenhouse for the fungus, forming a protective shell
where the organism can grow until it bursts a spore-bearing stalk
through the unfortunate insect's head. [ Gallery:
Zombie Ants ]

2. Suggestive Symbiosis

Ants aren't the only ones susceptible to mind-control invasions —
though for mammals, the mind control is slightly more subtle.
Take Toxoplasma gondii, a parasitic protozoa that wants
nothing more than to complete the sexual phase of its life cycle
inside of a cat. T. gondii can conduct the asexual phase
of its life cycle in other mammals (humans included), but it's a
genius at getting back into a cat if need be. For example, a
T. gondii­-infected mouse
loses its fear of cats, greatly increasing the likelihood
that it will be eaten by a hungry feline and that the parasite
can continue its life cycle unabated.

Humans can fall victim to T. gondii, too, and some
researchers suspect that the parasite might have links to human
mental health, including schizophrenia and
brain cancer. According to some scientists, a high enough
level of parasite infection in a society could
change the culture as a whole.

Back in the realm of fiction, "Star Trek" writers invented a
parasite with some striking T. gondii parallels. The
burrowing Ceti eel slithers into its human host's ear and lodges
in the cerebral cortex, rendering its host susceptible to
suggestion. In the long run, infection by a Ceti eel can lead to
madness — or death. [ Invasion
of the Alien Space Parasites (Infographic) ]

3. Alien Inspiration

The chest-bursting alien in Ridley Scott's "Alien" was inspired
by a real-life monster: parasitoid wasps. This group of wasps,
which encompasses multiple species, lay their eggs in
caterpillars, beetles, insects and other bugs. When the eggs
hatch, they crunch their way out of their living incubator just
like Scott's alien. One wasp species, Dinocampus
coccinellae, targets ladybugs,
which then sit on the wasp larvae like zombie nannies. The
partially paralyzed, but still living, ladybug hosts usually die
during this process. But about 25 percent survive, a 2011 study
found. That's a better rate than the cast of "Alien."

4. Sexual Infection

The 1975 movie "They Came from Within" (originally titled
"Shivers") features a parasite created by a mad scientist that
turns human hosts into violent, sex-crazed fiends. Appropriately
enough, the parasite can be transmitted via sexual activity.

Though it won't turn anyone into a sex zombie, a parasite called
Trichnomonas vaginalis can be transmitted via
intercourse. In fact, it's the cause of a very common sexually
transmitted disease called trichomoniasis. Only 30 percent of the
estimated 3.7 million Americans infected by this protozoa ever
develop symptoms, which include itching, burning and genital
inflammation. Luckily, a simple dose of oral antibiotics provides
a cure.

5. Willing Infection

Star Trek's Trill Symbionts were worm-like creatures that lived
in humanoid hosts from the planet Trill. These humanoid hosts
willingly took on their parasitic pals. In fact, joining with a
parasite was a competitive venture, with potential hosts having
to pass certain tests and be approved by a special commission.

Believe it or not, some real-life people intentionally infect
themselves with parasites, too. According to the
still-controversial hygiene hypothesis, an increasingly sterile
environment has led to a rise in autoimmune disorders
and allergies, including debilitating disorders like celiac
disease. Some brave pioneers have turned to helminthic therapy,
swallowing
parasitic worms in an attempt to get the immune system back
on track.

The treatment is not yet approved in the United States, but
researchers are working to understand whether it really works —
and how. One case study of a man with ulcerative colitis, a type
of inflammatory bowel disease, suggested that the worms
stimulate gut mucus production, easing symptoms. If
helminthic therapy proves helpful, perhaps the next generation of
science fiction films will cast parasites as not villains, but
sidekicks.